The present invention relates to improved sleeves or bladders for tire building machines for building tires.
In automated tire manufacturing process, the use of rubber bladders for forming tire bead packages and green tires is conventional in the art. The rubber forming the various tire components of the bead package and the green tire are in the uncured or green state In the manufacturing process. The turnup step employing the bladder is typically carried out at ambient temperatures (approximately 0xc2x0 to 30xc2x0 C.).
Bladders used in tire manufacturing must be elastomeric, have high elongation at break and must be capable of returning substantially to its original dimensions when stress is removed since it is subjected to repeated inflations and deflations. The bladder must have high durability, good cut resistance, and the outside surface should have good release properties, so as to minimize or eliminate sticking of the uncured rubber tire components to the outside surface of the turnup bladder.
Bladders have been made in accordance with several different methods. One such method of bladder construction is disclosed in U.S. Pat. No. 3,932,255 (Sarascan). Sarascan teaches covering the entire outer surface and a portion of the inner surface of a core of elastomeric material with a spray coating of polyurethane to obtain a desired thickness of the polyurethane layer. Following application of the liquid polyurethane, the sleeve is cured overnight prior to use.
U.S. Pat. No. 5,213,823 (Hunt) discloses that polysiloxane coatings have also been applied to create bladders with good release properties. Hunt teaches forming the bladder of a PVC material to obtain desired cut resistance and release properties.
For the two coated bladders, the manufacture of the bladder can be very time consuming.
The present invention is directed toward an improved bladder for use in tire manufacturing.
Molded and shaped polyurethane parts are dimensionally more accurate than compression molded rubber parts or hand built rubber/fabric parts as manufactured in present bladder manufacturing techniques. This improvement in accuracy can play a critical factor towards building a more uniform tire.
Additionally, many shapes and form are difficult to produce with the present bladders used in current tire manufacturing processes, requiring rubber gum-strips to be laid up on vertical surfaces and in accurate quantities to achieve complex shapes. The molds must be very strong to allow compressing the rubber and sustain the curing temperature. The present invention simplifies this considerably, as the polyurethane is liquid prior to polymerization. Mold costs are also reduced by the present invention.
Prior attempts have been made to incorporate polyurethane parts with building bladders, such as that disclosed by U.S. Pat. No. 4,168,336 (White et al). White et al teaches employing a separate T-shaped molded polyurethane part in combination with a pair of bladders for forming a bead and apex package. While this disclosed method assists in forming the bead package in the manner desired, the use of the molded part requires extra steps, including ensuring proper placement of the molded part, to achieve consistent manufacturing of the bead package.
The primary purpose of this invention is a turn-up bladder with superior dimensional precision in the area of bead clamping on the tire building drum by means of polyurethane parts and at the same time using the reinforced rubber structure in the inflating body of the turn-up bladder.
In the present invention polyurethane parts are bonded to rubber parts, the rubber may or may not be reinforced. In particular, the polyurethane parts used as part of a tire building turn-up bladder assembly together with a rubber inflatable body.
The present invention provides a bladder, useful in ambient temperature fabrication of rubber parts and components, having excellent release properties and resulting in improved manufacturing uniformity.
The present invention is an improved inflatable bladder for use in making an uncured rubber article on a building machine with which the bladder is associated. The bladder has an inflatable body portion with dimensions suitable for attachment in an operative relationship with a building machine. The bladder is defined by a first outer end and a second outer end relative to the operative relationship of the bladder with the building machine. The improved bladder is comprised of a rubber elastomer and polyurethane bonded to the rubber. The polyurethane portion is located at one of the ends of the bladder.
In one aspect of the present invention, the polyurethane comprising the polyurethane portion of the building bladder exhibits high tear and abrasion resistant properties. The polyurethane comprising the polyurethane portion of the building bladder may also be defined by its Shore A property, with a preferred Shore A hardness within the range of 25-85.
In one embodiment of the improved bladder, the polyurethane portion is ring shaped. The ring shaped portion is bonded in a recess of the rubber elastomer of the building bladder.
In a further aspect of the first embodiment of the improved bladder, the polyurethane portion has a width of 10 to 20% of the width of the bladder when the bladder is uninflated and mounted on the building machine.
In another aspect of the first embodiment, the second outer end of the bladder may also be provided with a similar ring-shaped polyurethane portion.
In a second embodiment of the improved bladder, the entire first outer end of the bladder may be formed from the polyurethane.
A further aspect of the second embodiment, the entire first outer end of the polyurethane portion of the building bladder has a width of 20 to 50% of the width of the bladder when the bladder is uninflated and mounted on the building machine.